O.S. Engines 21VG-PX - Manual (Page 9)

16
GLOWPLUG
The role of the glowplug
Glowplug life
Particularly in the case of very high performance
engines, glowplugs must be regarded as expendable
items. However, plug life can be extended and engine
performance maintained by careful use, i.e.:
Install a plug suitable for the engine.
Use fuel containing a moderate percentage of
nitromethane unless more is essential for racing events.
Do not run the engine too lean and do not leave the
battery connected while adjusting the needle.
With a glowplug engine, ignition is initiated by the
application of a 1.5-volt power source. When the
battery is disconnected, the heat retained within the
combustion chamber remains sufficient to keep the
plug filament glowing, thereby continuing to keep the
engine running. Ignition timing is 'automatic' : under
reduced load, allowing higher rpm, the plug becomes
hotter and, appropriately, fires the fuel/air charge
earlier; conversely, at reduced rpm, the plug become
cooler and ignition is retarded.
Apart from when actually burned out, a plug may
need to be replaced because it no longer delivers its
best performance, such as when:
When to replace the glowplug
Filament surface has roughened and turned white.
Filament coil has become distorted.
Foreign matter has adhered to filament or plug
body has corroded.
Engine tends to cut out when idling.
Starting qualities deteriorate.
Since the glowplug and fuel combination
used may have a marked effect on per-
formance and reliability, it would be
worthwhile to experiment with different plug types. An
O.S. No.8 glowplug is supplied with the engine. Rec-
ommended O.S. plugs are the No.8 and A5. Carefully
install plug finger-tight, before final tightening with the
correct size plug wrench.
17
ENGINE INSTALLATION
Make sure that the vehicle's engine mounting surfaces
are level and in the same plane. Poor installation may
cause distortion of the crankcase, bearings, etc.,
resulting in erratic running and loss of performance.
Chassis
Chamfer inside edges of bearers.
Do not allow
bottom of
crankcase to
touch chassis.
The recommended screws for securing the engine are
3mm or 4-40 steel Allen hexagon socket type.
If existing holes in the engine mount do not align
perfectly with engine mounting lugs, enlarge them
slightly with a needle-file so that screws are in
alignment with the mounting holes.
Engine Mount
When installing the engine on the chassis, note the
following points.
(Chamfer inside edges of bearers when the engine
mount edges interfere with the engine. Do not
chamfer the engine.)
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